This invention is directed generally to a small-sized printer of the type having a plurality of print rings with print characters circumferentially disposed therearound, and in particular to an improved detection arrangement for use with a small-sized printer of the type utilized in a desk calculator. The detector provides position signal pulses which control the entire print cycle including a stop signal for the motor which drives the print rings.
Miniaturized printers, of the type utilized to provide a permanent record in a desk calculator or other computing instruments, such as a cash register or the like, are characterized by the use of a drive motor which is energized during printing and de-energized when the printer is not in use. When the printer is in use a supply voltage is applied to the drive motor to effect an energization of the motor during a complete printing cycle of the printer. The printing cycle includes positioning of the print rings for printing, the printing operation, and return of the print rings to a standby position wherein each of the print rings is aligned in a rest position so that the next printing cycle can commence. Copending U.S. Patent Application Ser. No. 828,685 discloses a printer having mechanical features similar to the printer disclosed herein.
Due to the rapid speed with which the information can be processed by small-sized electronic instruments, such as desk calculators, electronic cash registers, and the like, it is desired that the entire printing cycle of the printer be completed at higher speeds with greater accuracy and at less expense. Heretofore, printers of the prior art have utilized two distinct detector arrangements for controlling the print cycle of the printer. In one type of apparatus, the detector includes a light emitting source and a photo-sensitive receiver element. A rotating disc having slots is rotated so as to intermittently intercept the light passage between the source and the light receiver. With such an arrangement a series of high quality pulses can be produced to control the print cycle. However, the constant current supplied to the light emitting diode, which generally serves as the light source, constitutes a high power drain. Such a detecting apparatus is shown in U.S. Pat. No. 3,148,616 by Miesiak, wherein a light source, a code disc and light-sensitive photo diodes are used in providing a detection system.
Another apparatus for detecting the position of print rings in a printer includes the use of rotating brushes and printed contacts on a circuit board. As the brushes pass over the contacts, signals are generated indicative of the position of the brushes and of the print wheels. Such an apparatus is shown in the U.S. Pat. No. 3,731,622 by Baranoff. By elimination of the light source and the photo detector, substantial savings are made in power consumption of the printer device. However, brushes and contacts produce less than a totally satisfactory signal output, in that chattering between the brushes and the contact points tends to produce erratic, irregular and noisy signals. Such signals when fed to the logic circuitry can produce erroneous outputs. Further, such chattering between contacts and brushes is a degenerative process which worsens with usage. Thus a detector using mechanical contacts and brushes, although it has low initial cost and continuously uses a low amount of power, has not been suited to printers of the type described herein.
Accordingly, what is needed is a detector having the low cost and low power consumption of mechanical brushes and printed contacts, combined with the reliability of a detector disc using a light source and photo-detector.